1. Field of the Invention
The present invention relates to an A/D converter device configured to take in a selected one of plurality of input signals through a multiplexer and converts it into a digital signal, and relates to an electronic control apparatus including such an A/D converter device.
2. Description of Related Art
Generally, an A/D converter device provided with a multiplexer for selectively taking in one of a plurality of input signals is configured to be supplied with a reference voltage such as a power supply voltage or a ground voltage, and to judge whether or not the A/D converter device (more specifically, the multiplexer or its A/D converting section) is functioning normally by detecting whether or not an A/D conversion result outputted from its A/D converting section coincides with an expected value corresponding to the reference value. For example, refer to Japanese Patent Application Laid-open No. 8-330959, or No. 10-115247.
However, such a conventional A/D converter device has a problem in that since it has to A/D-convert the reference voltage to judge whether or not there exists abnormality therein, it is difficult to assure a required control response in a case where it is used for an electronic control apparatus required to have a capability of sequentially A/D-converting input signals (sensor signals) at high speed, which are outputted from an engine control device and various sensors, because performing A/D conversion on the reference voltage delays A/D conversions on these input signals. It may occur that the above described problem can be solved if the A/D converter device is configured so as to make an abnormality judgment only once immediately after the electronic control apparatus in which the A/D converter device is included is powered on, or make am abnormality judgment only during a time period in which A/D conversions on the sensor signals are not required to be performed at high speed (for example, when a vehicle engine is running at low speed), or make an abnormality judgment only each time A/D conversions have been performed for a predetermined number of the input signals.
However, if the intervals at which the A/D conversion for making the abnormality judgment is performed is made longer than the intervals at which the A/D conversion on the sensor signals are performed, there arises another problem that when an abnormality occurs, the A/D converter device cannot detect it immediately, as a result of which the electronic control apparatus can control the control objects thereof in accordance with erroneous A/D conversion results.